Water-in-oil compound drop impact on a solid surface : numerical investigation

Details

Supervisors

Legat, Vincent

Faculty

Ecole polytechnique de Louvain

Degree label

Master [120] : ingénieur civil mécanicien, à finalité spécialisée

Abstract

\par A five months' research internship is performed in the field of multi-phase flows' dynamics, two important aspects have been intensively investigated: the jetting and spreading phenomenon of a compound drop. \par Compound drop impacting on a solid surface is of considerable importance in industrial applications, such as combustion, food industry, drug encapsulation and delivery. An intriguing phenomenon associated with this process is a singular jet that is dozens of times faster than its impact velocity, which has great significance to the design of industrial processes. \par In the present thesis, we numerically investigate the jetting and spreading process after a compound drop impacts a solid surface and compare the numerical results with experiments where a coaxial water-in-oil compound drop impacts a hydrophilic substrate with different releasing height and volumetric proportion. After impact, the water core spreads out as a lamella bordered by a rim, then capillary waves are excited ahead of the inward-propagating rim, and their superposition amplifies the fluctuations of the tip located at the axis of symmetry. Finally, the jet only consisting of oil is shot out at the instant of the collapse of the air cavity. \par Within certain range of water volumetric ratio, there are two peaks of jetting velocity, triggered by two different mechanisms to form a deep and cylindrical cavity that is necessary for high-speed jets. The time–evolution of the collapse in the first singularity regime yields to a $1/2$ power law, which could be derived from bubble pinch-off; while the latter one can could be understood as a balance between inertial and capillary forces, and behaves self-similarly as a power law of $2/3$. \par The maximal spreading diameter of of the inner water core of the compound drop is then studied. Comparisons with experiments, theoretical models and pure drop's spreading are done. The theory of $\beta_m\approx We^{1/4}$ is found and verified. Qualitative comparisons and conclusions have been deduced.